The use of radiation for treatment of portions of the human body is well-known in the medical field. Such radiation treatment includes the use of what are typically called linacs or linear accelerators. These devices provide a stream of electrons which may be used directly for therapy or in turn may impact a target material that can thereupon produce X-rays for irradiation of a particular body portion to be treated. In particular the treatment with radiation of intracranial portions of the human brain has been made practical by the use of stereotactic radiosurgery methods as developed by Professor Lars Leksell beginning in 1951.
The gamma knife developed by Professor Leksell is the standard for small-field irradiators. Intended for intracranial or brain irradiation, it consists of a spherical housing containing 201 cobalt sources which are aligned toward a single point in space at the center of the sphere. A set of collimation helmets with precisely drilled holes is provided and one or more of these helmets is used to provide the desired collimation. The precise drilling of the holes in these helmets allows the point of beam convergence to be well controlled.
The gamma knife is not, however, without its drawbacks. Because of these radioactive cobalt sources, the gamma knife includes large shielding structures which greatly increase the cost of construction and operation. As a piece of radiotherapy equipment it is also limited to the small number of patients that have suitable lesions which can be accommodated by the limited region of irradiation. In particular and for this reason, the gamma knife is currently restricted to brain irradiation for treatment of arteriovenous malformations and functional disorders. It has a relatively low dose rate requiring long irradiation times that increase as the cobalt source decays. In time, the array of cobalt sources must be replaced. This process is time-consuming and very costly.
In recent years, attempts have been made to use standard linear accelerators with special collimation systems to accomplish small-volume irradition, for example, in the brain. However, the use of conventional equipment systems for such irradiations suffer from two primary difficulties. First is the problem of achieving the geometric precision required, paticularly if volumes having only 3 or 4 mm cross-sectional diameters are to be irradiated as is often required in intracranial irradiations. This imprecision is due to the lack of structural rigidity inherent in currently available accelerators. Simply put, these machines and the patient support systems sag. In addition, there is the problem of achieving a reasonable or practical does rate when a small collimator aperture is used to provide the relatively small fields of irradiation required in this form of therapy.
I have invented an improved apparatus for treatment with radiation which employs accelerator technology to overcome the aforementioned problems and limitations.